The useful life of lumber intended for use in contact with the soil may be increased by impregnating the lumber with a preservative such as creosote or an oil-creosote mixture or the like. Railroad ties, for example, may be impregnated by treating the tie surfaces with a hot pressurized mixture of oil and creosote, the mixture penetrating for a distance into the ties. Penetration may be improved by forming incisions in the surfaces of the railroad ties before the impregnation step. Incisions are commonly made by passing the lumber through rollers having teeth extending from their surfaces, the teeth penetrating into the lumber parallel to its grain. Reference is made to U.S. Pat. Nos. 3,124,141, 3,709,271 and 4,137,956 for various devices for incising lumber in this manner.
The incisor teeth protruding from rollers such as those described in U.S. Pat. No. 3,125,141, are often broken during the incising operation because of the large forces involved. The teeth of incisor rolls such as those shown in U.S. Pat. No. 3,709,271 are provided with threaded shanks, and it would appear that such teeth can loosen or turn sidways out of alignment with the grain of the lumber.
The replacement of teeth in incisor rollers of the prior art has becomes a significant problem. For example, with the device of U.S. Pat. No. 3,125,141, one must remove the teeth and spacers from a channel formed in the roller until the broken tooth is able to be removed, following which a new tooth is inserted and the spacers and teeth are replaced in the channel. A threaded bolt urges the teeth and spacers together in place. In U.S. Pat. No. 3,709,271, which provides teeth with threaded shanks, tooth breakage at the shank causes the threaded shank to remain in its threaded socket in the roll, and removal of the shank may pose a difficult problem. With the roller of U.S. Pat. No. 4,137,956, replacement of a broken tooth entails removal of toothed rings and spacers from the circumference of the roller until the ring with the broken tooth is found, following which that entire ring must be replaced and the toothed rings and spacer rings must thereafter be carefully replaced on the roll.